1. Field of the Invention
The invention relates generally to the field of chip forming cutting tools utilizing indexable cutting bits or inserts. More particularly, the invention pertains to a spherical or ball nosed end mill having a cylindrical shank and mechanically held, multiple edge cutting inserts on its spherical cutting end with arcuate cutting edges for forming a radiused cut.
2. Description of the Prior Art
Ball nosed end mills are known which can perform omni-directional cutting and contouring of irregular shapes on workpieces. One class of such prior art tools features cutting edges integrally formed with the cutter body or cemented carbide cutting elements brazed onto the cutter body. Such designs require considerable manufacturing effort and their cutting edges can be reground or sharpened only with considerable difficulty and with the required use of suitable grinding machines. After regrinding, a loss of diametrical size occurs, necessitating careful machine adjustments when the reground tool is returned to service. Those tools with integrally formed cutting blades are of a single material and therefore are limited to use on certain narrow categories of workpiece materials. One such known brazed tool is disclosed in U.S. Pat. No. 4,132,493 -Hosoi, issued Jan. 2, 1979.
A second class of known ball nosed mills features indexable cutting elements or inserts. Such tools are disclosed, for example, in U.S. Pat. No. 4,175,896 - Kishinami et al., issued Nov. 27, 1979 and U.S. Pat. No. 4,252,400 - Mizuno et al., issued Feb. 24, 1981. The Kishinami et al. reference discloses an insert with a conical rake or chip engaging surface, while the Mizuno et al. patent teaches inserts mounted in a so-called "stand-up" position with each insert's minor dimension lying behind the cutting edge and receiving the cutting forces generated. Additionally, Mizuno et al. specifically teaches non-overlapping of the cutting zones of each insert employed in the cut. Milling cutters with inserts mounted in stand-up position require more mounting room thereby leading to lowered rigidity of the cutter body. Additionally, inserts in the stand-up mounting arrangement are subjected to maximum cutting forces through a minimum dimension of the insert body material. Cutters employing inserts with non-planar rake faces produce narrower, stringy chips of non-uniform width which are more prone to chip clogging conditions in the cut.